1. Field of the Invention
The present invention relates to an image sensor and related method with functions of repairing column readout circuits, and more particularly, to an image sensor and related method for repairing column readout circuits by shifting them in order on a group basis.
2. Description of the Prior Art
As the development of electronic products such as digital cameras and mobile phones progresses, the demand for image sensors increases accordingly. In general, image sensors in common usages nowadays are divided into two main categories: charge coupled device (CCD) sensors and CMOS image sensors (CIS). Primarily, CMOS image sensors have certain advantages of low operating voltages, low power consumption, and an ability for random access. Furthermore, CMOS image sensors are currently capable of integration with the semiconductor fabrication process. Based on those benefits, the application of CMOS image sensors has increased significantly.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a conventional CMOS image sensor 10. The CMOS image sensor 10 includes a pixel array 11, a column readout circuit array 12, a row decoder 13, a column decoder 14 and an analog to digital converter 15. The pixel array 11 includes pixel units P11˜Pmn arranged in a matrix form. Each of the pixel units P11˜Pmn has a light-sensing region and a peripheral circuit region (not shown in FIG. 1.) The light-sensing region is utilized for sensing incident light and accumulating photo charges that are generated due to the incident light. The peripheral circuit is utilized for properly outputting signals generated by the light-sensing region according to control signals of the row decoder 13 and the column decoder 14. The column readout circuit array 12 is arranged below the pixel array 11, and includes column readout circuits 120_1˜120_n. Each column readout circuits 120 is individually coupled to a corresponding column of the pixel array 11, and is utilized for reading signals outputted from the corresponding column. The analog to digital converter 15 is arranged on a side of the pixel array 11, and is utilized for performing signal processing such as analog-to-digital conversion for signals outputted by the column readout circuits 120_1˜120_n, successively.
As well known by those skilled in the art, each column readout circuit 120 can be a simple voltage or charge amplifier, or can further be realized by a correlation double sampling (CDS) circuit. However, if one or some column readout circuits in the column readout circuit array 12 have defects such as short circuit, open circuit or impedance mismatch due to fall of particles or process deviation during the fabrication process of the CMOS image sensor, causing such column readout circuits to not work normally, the entire column of pixels in the pixel array 11 corresponding to such column readout circuits cannot output correct signals accordingly. As a result, image quality of the CMOS image sensor is reduced, which increases the difficulty of following image processing, and even chip failure will occur.
Therefore, for the above-mentioned problem, US Patent Publication No. 2006/0261255, entitled “IMAGE SENSOR”, discloses an image sensor, which utilizes a redundant readout circuit as a backup for a column readout circuit having defects. However, such doings needs a massive decoder for addressing a location of the column readout circuit having defects in the column readout circuit array, resulting in that circuit area and production cost are increased significantly. Besides, since the entire column of pixels originally coupled to the column readout circuit that needs to be repaired is switched to couple to the redundant readout circuit located mostly outside the column readout circuit array, the output load of the entire column of pixels is increased significantly, such that differences between each column in the pixel array become larger, which leads to operation difficulties.